Testing for Varroa Mites
Varroa mites are one of the most significant threats to honey bee health today. Mites multiply quickly and spread bee viruses from bee to bee. The only way to control the deadly effects of viruses is to control the mites. Without proper management, mite-infested colonies have a very high probability of dying. Mites can also spread from colony to colony, on the backs of robbing and drifting bees, within a one-mile radius. That means that if you don't monitor and manage for mites, you may be putting your neighbors' bees at risk. In urban areas, horizontal transmission of mites (spreading mites) is an especially big problem. Read more about varroa mites here.
The Bee Squad encourages all beekeepers to monitor their bees for mites. Regular mite monitoring of your bees throughout the beekeeping season helps ensure that mite levels are low year round.
The two primary methods of sampling adult bees to estimate mite levels in a colony are the powdered sugar roll and alcohol wash.
University of Nebraska developed a testing method called the “powdered sugar roll.” The powdered sugar test is great because most of the bees in the sample survive (unless the bees get wet or are shaken too hard). Avoid using the powdered sugar shake in humidity or if the bees are bringing in lots of nectar. In these cases, the powdered sugar can dissolve and become sticky. We are marketing a powdered sugar mite testing kit called "MiteCheck Kits." These kits are reusable and comes with detailed user instructions.
The alcohol wash mite sampling method is more reliable with fewer variables that affect the efficacy as compared to the powdered sugar test (e.g., humidity that results in the sugar sticking to the bees, how hard the bees are shaken). For simple instructions on the alcohol wash see this guide. MiteCheck kits can easily be adapted for an alcohol wash. All you need is rubbing alcohol from a drug store and a solid canning jar lid.
MiteCheck Kits can be purchased from the University of Minnesota Bookstores. For bulk orders of at least 20 MiteCheck Kits, please email [email protected].
How low should mite populations be in your colony? Mite levels should be kept below 1 mites per 100 bees in the spring and 2 mites per 100 bees the rest of the year.
Treating for Varroa Mites: When & What?
All successful beekeepers manage varroa mites--it can’t be avoided. There are many ways to manage mites, some more complicated than others. This guide is intended for beekeepers who need a basic, tried and true method to keep their bees alive. As you build confidence and skill as a beekeeper, it is easier to experiment with other management methods that require advanced technique and knowledge of bee biology. Use the recommendations below to treat for mites in Minnesota. For instructions on HOW to treat, see the Honey Bee Health Coalition page on varroa management.
The most effective time to treat is when there is no brood in the colony as all the mites are on adult bees. Mites on adult bees are more easily killed; mites in brood are difficult to get rid of because the wax cappings on the brood cells protect the mites as they reproduce underneath. The hardest time to treat is when the colony has lots of brood. Treat in spring to help reduce the likelihood of high mite levels in late summer, when large brood nests make it hardest to treat effectively.
In May, June, August, and September, monitor varroa mites. Confirm that a treatment worked the way you hoped by sampling after a treatment.
The below treatment schedule is based on when the treatments are most effective and on mite and bee biology. This has been an effective method for us to manage mites and keep our bees alive! However, we cannot guarantee your colonies will not have additional issues with mites using this method. Monitoring often will help you catch unexpected spikes in your mite populations, and adjust your treatment plan accordingly.
Spring
- Package (suggested): Treat with oxalic acid (Api-Bioxal®) or Hopguard® 5 to 7 days after installing the package.
- Nuc: Ask the supplier if and how they managed mites in the spring. If they did not manage mites, treat for mites like you would an overwintered colony once the bees occupy a full deep box.
- Overwintered colony: treat with Mite Away Quick Strips®, Formic Pro®, or Apiguard®. Except for Mite Away Quick Strips® and Formic Pro®, treatment must be complete before honey supers are applied.
Summer
- Avoid treating colonies now unless mite levels are above 6 mites per 300 bees. Use Mite Away Quick Strips® or Formic Pro® as these products are safe to use with honey supers.
Before August 20
- Remove supers and treat with Mite Away Quick Strips®, Formic Pro®, Apiguard®, or ApiLife VAR®
- Check mites after treatment and every two weeks in fall to see that the treatment worked and if there is mite re-infestation from nearby colonies.
Fall when no brood is left in the colony
- Treat with oxalic acid (Api-Bioxal®) dribble in late fall. Can use Hopguard®, but remove the strips before winter.
Guidance on Using Mite Treatment Products
The below chart shows when each of the registered products can be used as mite control. Using the products when they are most effective can reduce the overall number of treatments used. Always read and follow the label.
*Oxalic acid vapor can be effective, but research suggests at least 2g oxalic acid per box is needed for the best efficacy, which is more than the legal label rate of 1g oxalic acid per brood box.